The venting of hydrocarbon vapors into the atmosphere has been a common practice at many petroleum production and processing facilities. Often, where the amounts are substantial, the vapors are collected, recompressed and used. There are many other locations where these vapors are vented to the atmosphere. Recently, as of 2012/2013, the United States Environmental Protection Agency (EPA) has placed an upper limit on the amount of volatile organic vapors (VOCs) that may be vented. There is also a desire to minimize the venting of methane gases or gases that decompose to methane to the atmosphere because methane has a strong greenhouse gas heat trapping effect, being twenty-one times more effective than carbon dioxide over a 100 year period.
Vent gases originate from petroleum liquids that are stored in one or more tanks. These storage tanks can be fitted with pressure relief devices that allow the gases to escape to the atmosphere if a specified pressure is exceeded. To prevent the escape of the vent gases to the atmosphere these vent gases are directed to a burner system that consumes the tank gas vapors at a pressure below the pressure relief set-point.
An effective method to deal with the vented gases is to combust the gases under controlled circumstances. The standard method of combusting these gases is to feed these gases to an incinerator unit or flare where a pilot, either continuous or started on demand, feeds into the vented gases in the presence of air to ignite the gases. In the case of a flare, the vent gases are directed through a vertical tube or pipe and burned as the gases contact air. Since a flare is undesirable from an environmental and public perception point of view, the general preference is to enclose the flame and to regulate the air flow to achieve combustion with good air-fuel ratio control. The disadvantage with Flares and incinerators is that the heat energy from the vapor combustion is lost and not used. In addition, adding a flare or incinerator to a site may require additional effort to obtain permission for installation and operation by regulatory authorities.
In many of the petroleum production processes natural gas mediums such as fired heater units are employed for a multitude of purposes. Such heaters are used on an intermittent basis in response to the process requiring the heat energy and as a result are not always available to combust the vent gases. Typically these heaters use a burner jet where the fuel is introduced and a horizontal fire tube for directing the flame and the hot combustion gases to the medium requiring the heat and then to a vertical stack for directing the exhaust gases to the atmosphere. The horizontal portion may be simply one pipe or several parallel pipes connected to a stack, a U arrangement or a multi-pass arrangement where the pipe or pipes make several passes through the medium to be heated. The use of heaters can provide an effective solution to using vent gases however varying demand requirements can result in times when heating of the medium is not required and the vent gases must be dealt with.
Accordingly, systems and methods that enable a novel way of combusting excess vent gases when a main burner is not in operation remains highly desirable.
It will be noted that throughout the appended drawings, like features are identified by like reference numerals.